The present invention relates generally to a thermal print head and more particularly to a thermal print head wherein a driving integrated circuit (IC) and a printed circuit board (PCB) are manufactured on a boat instead of on a heat sink.
A thermal print head converts electric information to thermal energy to record the information on a recording media such as thermal recording paper by discoloring the recording media according to the electric information.
Referring to FIG. 1, a conventional thermal print head is illustrated. As shown in the drawing, the conventional thermal print head includes a substrate 5 on which a heating element 2 and a number of driving ICs 7 for driving the heating element 2 by providing thereto an electric signal are mounted, a PCB 10 for providing the electric signal to the driving IC 7, and a number of gold wires 6 for connecting the driving ICs 7 with the electric signal generated from the PCB 10. The substrate 5 and the PCB 10 are commonly mounted on a heat sink 4. The PCB 10 is electrically connected to the heating element 2 through a common electrode 1 and a number of individual electrodes 3. It is necessary that the substrate 5 on which the heating element 2 is to be mounted should be made of a material which is stable against the high temperature and the chemical reaction during the manufacturing process. Generally, a material containing 96% or over 96% of Alumina Al.sub.2 O.sub.3 is used to make the substrate 5. Glaze of 60 .mu.m thick is coated uniformly on the alumina substrate to effectively charge and discharge the heat generated from the heat element 2 according to the current flow on the substrate. A resistive film with a specific resistance is formed on the glaze layer to generate the heat according to the current flow. The resistive film is about 1000.ANG. thick. A wiring layer (usually made of aluminum) through which the electric current flows is formed on the resistive film. The heating element and the electric wiring circuit having a specific shape are then formed by means of the photo-etching technique which is generally used for manufacturing the semiconductor devices. In order to prevent the oxidization of the heating element and the abrasion of the heating elements due to the contact with the recording media such as a thermal recording paper, a single layer of nitride-silicon or a double layer made of an oxide layer and a titanium layer is coated around the heating elements and the wirings. Alternatively, the sputtering or CVD (chemical vapor deposition) method can be used for forming the films. The foregoing processes will conclude the manufacture of the heating elements.
Referring to FIG. 2, shown is a cross sectional view of a conventional thermal print head which is manufactured by a gold wiring connection technique. It is shown in the drawing that the substrate 5 on which the driving IC 7 and the heating element 2 are mounted, and the PCB 10 are mounted on the heat sink 4 and those are electrically connected to each other by a gold wiring connection technique. Further, the driving IC 7 and the gold wire 6 are covered by resinoid 12 and 13 (preferably silicon rubber) thereby to protect the gold wire 6 from external phenomenon and vibration. Finally, a protection cap 14 for protecting the gold wire 6 and the driving IC 7 from the external impact, a connector 9 for connecting the electric signals, the heat sink 4, a thermistor (not shown) for measuring the circumference temperature, and a condenser (not shown) for preventing the external noises are assembled together to complete the manufacture of the thermal print head.
Another conventional method for manufacturing the thermal print head has been proposed. According to the method, after a driving IC is mounted on a substrate on which a heating element is formed, electrical connections between the substrate and the driving IC are all made on the substrate. Thereafter, by use of a flexible PCB, the driving IC is connected with the external signals.
In the case of the thermal print head according to the former technique in which the substrate on which the heating elements and the driving IC are formed, and the driving PCB are assembled on the heat sink, the heat sink plays a role of a mechanical fixing media which fixes the thermal print head on a system, the shape and material of the heat sink must be changed according to the system to which the thermal print head is to be installed. Therefore, the method for manufacturing the thermal print head has to be changed according to the shape and material of the heat sink and there was a problem that different types of jigs must be prepared for the different systems. On the other hand, in the case that the electrical connections are all embodied on a substrate on which the heating element are formed, although the manufacturing method is more adaptable to the mechanical change of the system, the size of the substrate becomes as large as the size of the driving IC and the electric wiring portion thereby results in increasing the cost for manufacturing the thermal print head.